The present invention relates to a method for fabricating a semiconductor device and substrate processing apparatus; and, more particularly, to a semiconductor device fabricating method and a substrate processing apparatus capable of depositing a boron doped polycrystalline silicon-germanium film or a boron doped amorphous silicon-germanium film by means of a low pressure CVD (Chemical Vapor Deposition) method.
A low pressure CVD method has been widely used in forming thin films in the course of fabricating semiconductor devices, e.g., IC, LSI or the like. Such thin film forming processes include depositing of a silicon-germanium film on a substrate.
Silicon-germanium is employed in growing an epitaxial base region of a heterojunction bipolar transistor (HBT) and forming a polycrystalline silicon-germanium film as a portion of a gate electrode of a MOS transistor.
In a conventional polycrystalline silicon-germanium film forming process by a vertical type low pressure CVD apparatus, diborane (B2H6) is used for doping boron. Since, however, the gas phase reaction of diborane is rather strong, diborane reacts not only with wafers but also in other portions of a reaction chamber. Further, since boron is readily doped in a deposited film, a consumption rate thereof is great. Accordingly, the uniformity in boron concentration within a wafer and between wafers is deteriorated.
That is, since diborane is rapidly depleted, the concentration thereof becomes less at the downstream side thereof. Consequently, inter-wafer uniformity of boron concentration becomes degraded. In order to solve the foregoing problem thereof, i.e., to improve the boron concentration uniformity, it becomes necessary to install a plurality of diborane gas supplement nozzles in an inner space of the reaction chamber, to compensate for the rapid depletion of the diborane gas.
Further, as the diborane gas flows toward a central surface portion of a wafer, the diborane gas is continuously consumed and thus the concentration thereof is getting less, resulting in the nonuniformity in the boron concentration within a single wafer. The uniformity of boron concentration within a wafer can be improved by increasing a gap between wafers.
However, further, in case of growing SiGe films, in addition to the diborane gas supplement nozzles for doping, a number of monogermane (GeH4) gas supplement nozzles are also required to ensure intra-wafer and inter-wafer Ge concentration uniformity. In such a case, the number of nozzles and mass flow controllers for controlling flow rates are undesirably increased. In addition, when the gap between the wafers increases, the number of the wafers which can be processed at one time is reduced. For example, when the gap between the wafers becomes double, the number of the wafers which can be processed at one time is reduced to one half.
It is therefore, an object of the present invention to provide a semiconductor device fabricating method and a substrate processing apparatus capable of depositing a boron doped polycrystalline silicon-germanium film or a boron doped amorphous silicon-germanium film by means of a low pressure CVD method, while maintaining an improved uniformity in the boron concentration without requiring a number of gas supplement nozzles for supplying a doping gas.
In accordance with a preferred embodiment of the present invention, there is provided a semiconductor device fabricating method for forming a boron doped silicon-germanium film on one or more substrates in a reaction furnace of a low pressure CVD apparatus, including the steps of: loading said one or more substrates into the reaction furnace; supplying GeH4 and SiH4 as a reaction gas to the reaction furnace; and supplying BCl3 as a doping gas to the reaction furnace.
In accordance with another preferred embodiment of the present invention, there is provided a substrate processing apparatus for forming a boron doped silicon-germanium film on a wafer, including: a reaction tube in which at least one substrate is processed; a heater for heating said at least one substrate in the reaction tube; a first gas supplying line for supplying SiH4 to the reaction tube; a second gas supplying line for supplying GeH4 to the reaction tube; and a third gas supplying line for supplying BCL3 to the reaction tube.